This invention relates to a latching mechanism and more particularly to switches, writing instruments and the like which are round in configuration and require a latching function.
Round push-button switches are used for keyboard shifting on computers, typewriters or the like and as panel mounted devices for instrumentation, electronics and controls. The known round push-button switches which provide a latching function have drawbacks, however. Two of these problems are difficulty in assembling the latching mechanism and reliability of the latching mechanism.
Round cylinder switches provide an advantage in that opposite sides of a switch plunger can be simultaneously locked down. Having two sides simultaneously locked down increases the reliability of the switch and also makes the plunger rest level in the latched position. U.S. Pat. No. 3,437,775 to Piber discloses a round push-button switch including a cammed surface liner inserted into a circular housing. Piber also includes a continuous collar which rotates on a carrier and includes round lugs. The round lugs of the collar engage the cammed surfaces of the liner.
There may be, however, a difficulty in assembling the Piber structure, because one has to line up and position separate cam surfaces within the housing to obtain an interior portion having cam surfaces. Where the rolled liner is joined in the housing interior, one may introduce a discontinuity, ridge or seam to the cam surface. Such a discontinuity at the rolled up ends of the cam surface could interrupt or hang up a lug during ring rotation. Also, assembly of the continuous ring onto the collar may be difficult and time consuming. Further, the point-to-point contact between round lugs and saw teeth cammed surfaces is not as reliable as desired.
In a traditional ballpoint pen mechanism, the center plunging member rotates by following a saw tooth pattern molded into the housing to create a lock-down function. For example, U.S. Pat. No. 3,051,132 to Johmann does not have a separate rotating latching ring. Instead, the entire spring loaded cam shaft is rotating. Thus, one may not be able to advantageously use the rotating cam shaft for other functions such as contacting fixed position terminals for reliably closing a circuit.
Also, traditional ballpoint pen mechanisms normally have a freely floating button so there is no indication from the switch position of when it is in the on position.
The present invention is directed towards eliminating deficiencies found in the above-identified prior art.